Sept7 M3-Pelvis_Anatomy_lecture_5 Flashcards
borders of the anal triangle
- ischial tuberosities (imaginary line between them)
- sacrotuberous ligaments
- coccyx
ischiorectal (ischioanal) fossa is what
two triangles on either side of the anus mostly filled with fat + levator ani
(imp) borders of the ischiorectal fossa
- base (superficial) = skin
- lateral wall = lower part of obturator internus
- medial wall = levator ani
- fossa continuous with the deep perineal pouch (of the UG triangle). nothing separating them. for deep perineal pouch, superficial base was perineal membrane and deep base was also levator ani
structures visible in a coronal view of the ischiorectal fossa
- anal canal (middle)
- levator ani (medial wall of the fossa + going oblique and upwards laterally)
- lot of fat below, lat to levator ani (fat pad)
- obturator internus (lateral wall of the fossa)
- pudendal canal (just medial to obturator internus, contains pudendal vessels and n)
- Colle’s fascia (superficial fascia marking start of the superficial base). extends from ischium to anal canal
- skin (base)
anal canal structures in coronal view
- levator ani
- anorectal junction (end of smooth features of rectal ampulla. is end of the rectum
- anal columns and sinuses below the ARJ (like prostatic crests on either side of prostate and sinus in middle). are in the anus
- anal valve = narrowing of anal canal at level of the bottom of the anal sinuses and columns
- pectinate line = line between endoderm-derived hindgut (above) and ectoderm-derived anal pit (below)
- anal pecten (region between pectinate line and anocutaneous line)
- anocutaneous line (division between anus and skin)
clinical significance of the pectinate line in the anal canal
- internal hemorrhoids are above it and are not painful
- external hemorrhoids are below it and are painful
muscles surrounding the rectum
- inner circular layer
- outer longitudinal layer
2 anal sphincters and what they cover
internal anal sphincter (more medial): covers upper two thirds of anal canal)
external (more lat): covers lower two thirds of anal canal)
the two overlap in the middle third of the rectum
control of anal sphincters (which is voluntary?)
- internal = involuntary. always contracted, SS tone
- external = voluntary (somatic inn in this region is from pudendal n, which gives inferior rectal nerves)
internal anal sphincter is what
muscle of inner circular muscular coat around rectum coming down around anal canal
external anal sphincter is what
levator ani coming down reaching kink of rectum (of puborectalis sling)
3 parts of the external anal sphincter
top to bottom
- deep
- superficial
- subcutaneous
bloody supply to the anus
inferior rectal a and v coming from internal pudendal a and v (which come from internal iliac a and v)
inn to anus
inferior rectal nerves coming from pudendal n
pudendal canal (Alcock canal) def + is where
- a passageway within the obturator fascia (fascia of obturator internus) on lat wall of ischiorectal fossa) for the internal pudendal a and v + pudendal n
- is inferior to the obturator foramen
how to see internal pudendal a from the gluteal region
look for ischial spine (look underneath the area of the inferior gluteal a)
what internal pudendal a does after swings back in perineum around ischial spine
travels forward to reach the UG triangle (travels on side of ischiopubic ramus, below obturator foramen)
diff arteries that come off the internal pudendal a as it goes in the pudendal canal
- start (in the back): gives off inferior rectal a
- end (front): gives off perineal branches that go in deep and sup perineal pouches
- distally becomes the dorsal artery of the penis or clitoris
why coccygeus m. is a key point in the pelvis
- points to the ischial spine
- is deep to the SS ligament
- start of the tendinous arch
internal pudendal a travels where with respect to coccygeus
below piriformis (medial to it), above coccygeus (lateral to it)
PNS divisions
- sensory (afferent): somatic + visceral
- motor (efferent): somatic + ANS (visceral)
lumbar plexus nerves fct in general
-motor (somatic and ANS) and sensory (somatic and visceral)
lumbar plexus nerves, parts of interest
- lumbosacral trunk (L4 and L5) = uppermost part of the sciatic nerve
- obturator n (L2,3,4) (through obturator canal to medial thigh muscles and skin)
sacral plexus: where levels S1,2,3,4 come from anatomically
come out of the anterior sacral foramina
ventral rami of sacral plexus are where in the pelvis
on top of piriformis
dorsal rami go to the back
sciatic n levels + is what two nerves later
L4 to S3. comes out above piriformis in greater sciatic foramen
- common fibular n
- tibial n
pudendal n levels and fct
S2,3,4
- motor (somatic and ANS)
- sensory (somatic and visceral)
how not to confuse lumbosacral trunk with the S1 level
lumbosacral trunk crosses the ala of the sacrum and NOT the sacral promontory
where are the sacral nerves in the pelvis
above piriformis (makes sense bc said before that ventral rami are above piriformis)
regions where the pudendal n is travelling
- pelvis (S2,3,4)
- gluteal region
- pudendal canal (start of canal = gives off hemorrhoidal (inferior rectal) n). middle of canal gives off perineal n.
- deep perineal space
- dorsum of the penis (where becomes dorsal n of the penis). travels with the deep dorsal arteries (from dorsal penile a) + the deep dorsal veins between Buck’s fascia and the tunica albugenia
inferior rectal n and a path taken
- leave the pudendal a and n but stay in the pudendal canal
- leave the pudendal canal
- go towards the anal sphincter
PSS innervation of the pelvis
pelvic splanchnic nerves
- originate from ventral rami of S2,3,4
- travel on each side of pelvis THROUGH inferior hypogastric plexus (a SS structure) (on lat rectal and bladder walls)
- after reach lat rectal wall, go to distal third of transverse colon, sigmoid colon, rectum, bladder, genitalia. preganglionic fibers synpase in the walls of the organs
- don’t synapse in hypogastric plexus*
SS innervation to pelvis
sup and inf hypogastric plexi
- white rami communicantes go from spinal cord to SS trunk ganglia from T1 to L2 (T5 and below don’t synapse there). the chain continues below L2 height until S3
- these two plexi arise from the lowest levels of the SS chain
- pregang fibers synapse in the inferior hypogastric plexus**, then go to organs via blood vessels pathway
hypogastric nerves def
nerves between the ONE superior hypogastric plexus in the body and the TWO inferior hypogastric plexi (one on each side). so there are TWO hypogastric nerves
what SS fibers synapse in the sacral part of the SS chain
postganglionic fibers that start at the SS chain (sacral) and that travel through rami levels S2,3,4 to leave the pelvis via the sacral foramina and reach the sciatic nerve
sacral splanchnic nerves def
sympathetic nerves extending from the SS chain ganglia to the inferior hypogastric plexus
where to recognize pelvic splanchnic nerves if can find them
back wall of pelvis, on sacrum, exited sacral foramina with the sacral nerves
SS inn to the leg is done how
postgang fibers leaving hypogastric plexus reach a sacral nerve (S1) (or postgang fibers leaving SS chain and going to sciatic n) and go to the leg
SS inn of the pelvis comes from which nerves and plexus
- SS chain to sacral splanchnic nerves going to hypogastric plexus
- SS chain to sup hypogastric plexus to hypogastric nerves to inferior hypogastric plexus
superior hypogastric plexus is located where
over the aorta at level of bifurcation
sacral sympathetic chain relates to what nearby structure in the pelvis
is below the lateral sacral a
how to recognize pelvic splanchnic n vs sacral splanchnic n
- sacral splanchnic n leave the SS chain ganglia
- pelvic splanchnic n come off the sacral n and go out
